Cooperation can be advantageous in nature, for example hunting together, protecting territories, and raising young. However, in the wild, a monkey must be very careful about who it collaborates with. A cooperation partner much higher in the hierarchy might simply decide to keep the obtained food for itself. The choice of a partner is therefore of great importance. But new research now shows that monkeys make different partner choices depending on the number of locations available for cooperation.
Behavioural biologists from Utrecht University and the University of Veterinary Medicine in Vienna gave a group of long-tailed macaques one or more apparatuses at which they could work together. If two monkeys pulled a rope from the apparatus, they could pull a reward towards themselves. When the researchers placed only one apparatus, the monkeys were much more selective about who they collaborated with. But as soon as the scientists provided multiple cooperation apparatuses, the monkeys became much less selective about who they wanted to work with.
Jeroen Zewald, co-author on the study, notes “Imagine, for example, that you are hunting a deer together for food, but this is the only prey in the area. In that case, you want someone you can use, but who doesn't keep the prey for themselves after the hunt. Partner choice is therefore of great importance. Whereas if there is a whole herd of deer roaming around, it is less important who you choose, because there are always other deer to hunt if someone steals the prey anyway. The monkeys also showed this difference in choice.”
Professor Liesbeth Sterck, co-author and primatologist at Utrecht University, explains why this finding is so important. “Normally, in research into cooperative partner preferences in animals, only one apparatus is given to a group of animals, which is therefore easily claimed by one or two individuals. This creates a very specific situation for partner preference, whereas this is not always the case in nature. Consider, for example, fruits or leaves that can be found in multiple places in the forest. It is therefore important to see that different situations can lead to different partner preferences.”
Although in this study the monkeys did not appear to actively select their partners by asking them for help or waiting for them, their preference seemed to be based primarily on who they tolerated in their proximity. Many other primate studies have also shown the importance of social tolerance for cooperation, but the change in their preference due to the number of devices had not been demonstrated previously. It will therefore be important to include this in new studies to learn more about who animals want to cooperate with and which situations this depends on.
The article "Zewald, J. S., et al., (2026) Monopolization and cooperation: number of locations affects cooperation and partner preference in long-tailed macaques” was published in Animal Behaviour.
Rückfragekontakt:
Jeroen Zewald, MSc.
Messerli Forschungsinstitut/Goffin Lab
Veterinärmedizinische Universität Wien (Vetmeduni)
Jeroen.Zewald@vetmeduni.ac.at